The aim of this project is to understand the mechanism by which the rat liver organelle, the peroxisome, is formed. The organelle is involved in the metabolism of hydrogen peroxide, the B-oxidation of fatty acids, and the oxidation of ethanol. Isotopic labeling, cell fractionation, biochemical analyses, immunochemical precipitations, cell-free protein syntheses, and protein chemistry will be employed. We will prepare antisera against various peroxisomal proteins. We will inject rats with 3H-leucine, wait various lengths of time, and remove and fractionate the livers by differential and sucrose gradient centrifugation. The fractions will be analyzed enzymatically to locate the marker enzymes and thus the organelles. The various peroxisomal proteins will be isolated immunochemically from the fractions and their radioactivity measured, in order to trace the intracellular pathway followed by these proteins from their site of synthesis to the peroxisomes. Similar experiments will be carried out in rats treated with the hypolipidemic drug, clofibrate, which greatly increases the abundance of peroxisomes. We will characterize catalase by peptide mapping, amino acid composition, partial amino acid sequence and content of sugar, in order to see whether it contains any unique structural features that could account for its specific sequestration in peroxisomes, and whether its structure undergoes any modification during or after its entry into peroxisomes. The properties and subcellular location of the messenger RNA for catalase will also be investigated.